Perianal fistulas, also known as anal furunculosis, can be a severely debilitating condition in dogs, characterized by painful, ulcerated tracts or tunnels around the anus. While most dogs respond well to timely therapy, understanding the condition, its causes, and the role of diet is crucial for effective management. This article provides a comprehensive overview of perianal fistulas, with a special focus on the importance of diet in managing this challenging condition, particularly in predisposed breeds like German Shepherds.
What are Perianal Fistulas?
Canine anal fistulas or anal furunculosis, is a condition in dogs that causes painful, ulcerated tracts or tunnels around the anus. These tunnels can be deep and may extend inward, causing discomfort and inflammation. A perianal fistula is a hole near the anus that shouldn’t be there. Sometimes there are only one or two small holes, and other times an affected dog may have many large, draining holes that look like ulcerated wounds near their anus. The anus is the opening of the rectum through which stool passes when a dog has a bowel movement. When a perianal fistula develops, pet parents may notice a small hole or drainage near the anus. This hole is actually a tract, or tunnel, that isn’t normally there.
Dog anal fistulas can be a chronic and recurring condition, affecting certain breeds more commonly, such as German Shepherds, Irish Setters, Boxers, and Bulldogs. When the condition is mild you may not notice there is a problem, but as it continues to progress watch for signs your dog is straining to defecate, having blood in their feces, and a decrease in appetite. Mild perianal fistulas may just appear to be a pustule with erosions. Severe cases can be bleeding sinus cavities with several draining tracts oozing blood and pus.
A canine anal fistula is an abnormal connection or passageway that forms between two organs, vessels, or structures in the body that are not normally connected. This connection creates an unnatural channel, allowing fluids or substances to flow between these structures. Fistulas can occur in various parts of the body, not just the perianal area. Anal sac fistulas are abnormal connections or tracts that form between the anal sacs and the skin surrounding the anus.
Breeds at Risk
Although most cases are in German shepherd dogs, any breed can be affected. Other breeds include but are not limited to Shih Tzu, Pembroke Welsh corgis, boxers, Labrador retrievers, and mixed breed dogs. Position of their tail, which is often carried low between the hip bones, covering the anus, is thought to be a predisposing factor. A genetic component is likely, with German Shepherds being the most commonly affected breed.
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Signs and Symptoms
Clients most commonly report tenesmus, hematochezia, dyschezia, frequent small volumes of feces, perianal licking, and purulent discharge. When the condition is mild you may not notice there is a problem, but as it continues to progress watch for signs your dog is straining to defecate, having blood in their feces, and a decrease in appetite.
A thorough examination of the rectum and anus will reveal mild to severe sinuses, draining tracts, and ulcerations surrounding the anus.
Diagnosis
If the patient is a German shepherd, a perianal fistula is most often diagnosed on the basis of clinical presentation and physical examination alone. If the dog is another breed, other causes based on clinical signs should be ruled out first. For example, for a Shih Tzu with purulent anal discharge and intracellular cocci seen with cytology, the proper first step would be treating the infection to see if the draining tract resolves.
The vet will likely palpate the anus, the fistula, and the anal sacs. Several conditions need to be ruled out to determine if your dog has a perianal fistula. Your veterinarian may recommend bloodwork prior to starting treatment, to ensure your dog can tolerate the oral medications that may be recommended.
Taking a biopsy sample of the draining tract can help detect other causes (e.g., cancer, allergies, foreign body) and obtain a definitive diagnosis. However, although biopsy is the best way to confirm a diagnosis, it is rarely performed due to the potential complications, similar to the complications of surgery.
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Differential Diagnosis
Differential diagnoses vary greatly, depending on the presenting clinical signs. If the only signs noted are perianal pruritus, then other differentials include allergic dermatitis (atopic dermatitis and adverse food reaction) and anal sac abscess. If the patient has tenesmus and hematochezia only (no draining tracts or visible fistulas), the primary differentials become gastrointestinal conditions (e.g., inflammatory bowel disease, intestinal parasites, rectal strictures).
The Importance of Timely Intervention
Timely diagnosis and institution of appropriate therapy are critical. Lack of or unsuccessful treatment for any length of time carries the potential for formation of anal stricture and large, deep fissures, which can decrease the patient’s quality of life.
Potential Causes of Perianal Fistulas
The exact cause of canine anal fistulas is not fully understood, but several factors are believed to contribute to their development:
- Immune System Dysfunction: An abnormal immune response is thought to play a significant role in the development of perianal fistulas. While the exact cause of perianal fistulas is not known, it is suspected to be an autoimmune disease-where the immune system is mistakenly attacking healthy cells and tissue.
- Dietary Factors: Some research has suggested a potential link between diet and perianal fistulas.A possible link has been identified between perianal fistulas and food allergies in pets.
- Genetics: A genetic component is likely, with German Shepherds being the most commonly affected breed.
- Anal Sac Involvement: The anal glands, also known as anal sacs, may or may not be involved. Infection of these sacs may lead to an increased risk in developing perianal fistulas.
The Role of Diet in Managing Perianal Fistulas
A possible link has been identified between perianal fistulas and food allergies in pets. Whether there is a direct correlation of these diseases or the dogs just happened to have 2 concurrent diseases is unknown. Regardless, use of a novel protein diet or hydrolyzed diet has been beneficial for some patients. Diet Changes - A hypoallergenic, novel protein diet may help support your dog's overall health and immune system. Some pet owners have reported improvement in perianal fistula symptoms by avoiding common allergens or inflammatory ingredients.
Given the potential link between diet and perianal fistulas, dietary management is often a crucial component of a comprehensive treatment plan.
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Key Dietary Considerations
- Novel Protein or Hydrolyzed Protein Diets: These diets are designed to minimize allergic reactions by using protein sources that the dog has never been exposed to before (novel protein) or proteins that have been broken down into smaller pieces (hydrolyzed), making them less likely to trigger an immune response.
- Elimination Diets: These diets involve feeding a very restricted diet for a period of time to see if symptoms improve, helping to identify potential food allergens.
- Avoiding Common Allergens: Common allergens for dogs may include grains, beef, and chicken.
- Minimizing Additives and Preservatives: Artificial additives and preservatives can contribute to inflammation.
- Natural and Minimally Processed Foods: Using a natural, minimally processed diet with fiber in the form of vegetables and pumpkin can help.
- Fiber: Fiber in the form of vegetables and pumpkin can help.
Additional Dietary Support
- Probiotics: Probiotics are beneficial bacteria that support digestive health and balance the immune system. Probiotics can help maintain a healthy gut microbiome, which can reduce inflammation and modulate your dog's immune response.
- Plant Sterols: Plant sterols have been studied for potential health benefits, such as anti-inflammatory effects and immune modulation. By balancing the immune response and reducing inflammation, plant sterols may help alleviate symptoms associated with perianal fistulas. Perianal fistulas in dogs are often considered to have an autoimmune component, and plant sterols (phytosterols) can be helpful in managing autoimmune conditions due to their immune-modulating properties.
Treatment Options Beyond Diet
A wide variety of treatments for perianal fistulas have been performed. Dating back to the 1940s through 1970s, perianal fistulas were initially believed to be exclusively a surgical disease. Surgery usually included resection of all diseased tissue with or without removal of the anal sacs. This procedure could involve anywhere from a focal area of resection all the way up to a 360-degree resection with anoplasty. When a perianal fistula was believed to be associated with low tail carriage, amputation of the tail was also described as a treatment but is no longer recommended. The use of laser for surgical excision has been described, as has cryotherapy to ablate the diseased tissue. Typically, patients are given a stool softener postoperatively to lessen the pressure during bowel movements and to allow the area to heal. A common problem with surgery as the sole therapy is the lack of resolution and high incidence of recurrence. Surgical complications are also a significant problem and include wound dehiscence, flatulence, fecal incontinence, diarrhea, tenesmus, constipation, and rectal strictures. A wide variety of immunosuppressive therapies, as either monotherapy or a combination of therapies, have been used to treat perianal fistulas. Most patients will need long-term immunosuppressive treatment to keep the disease in remission.
While diet plays a crucial role, it is often necessary to combine it with other treatment modalities for effective management of perianal fistulas.
Medical Management
- Immunosuppressive Medications:
- Cyclosporine is one of the drugs the author uses most often for this disease. Several studies have reported significant improvement of perianal fistulas treated with cyclosporine (96% to 100%). The dosages used in studies are variable, ranging from 4 mg/kg PO q24h to 10 mg/kg PO q12h initially, which may account for some of the reported failures at the low end of the dose range. The author typically aims for the immunosuppressive dose of 7 mg/kg q24h. The cost of cyclosporine is a limiting factor that can be reduced if given with ketoconazole. The typical combination dosages the author uses are cyclosporine at 3.5 mg/kg q24h and ketoconazole at 5 mg/kg q24h, each with a meal. Before altering drug doses, some veterinarians evaluate trough levels of cyclosporine or molecular assays to evaluate the level of immunosuppression. Although this topic is debatable, the author believes it is a viable option when appropriate doses of cyclosporine have been given but clinical effectiveness is lacking. Cyclosporine is generally well tolerated and the incidence of side effects is low, especially when the drug is given with a meal or frozen before administration.
- Immunosuppressive doses of prednisone (2 to 4 mg/kg PO q24h) have been described as effective, with 33.3% of patients achieving complete remission, 33.3% showing improved clinical signs, and 33.3% showing no improvement. A benefit of prednisone therapy is its quick onset of action compared with other immunosuppressive therapies; the problem with prednisone therapy is long-term side effects. This drug, in combination with metronidazole, has been reported to effectively decrease the size of the perianal fistula before surgical removal of residual disease. Prednisone is a steroid that can be dosed at high levels to treat perianal fistulas. While steroids are inexpensive compared with other medications, they have side effects that pet parents may find frustrating. It is very common for dogs on prednisone to drink more, pee more, eat more, and pant more.
- Azathioprine: This immunosuppressive medication can be used to shrink the perianal fistula prior to surgery or can be used to treat the condition without surgery. Azathioprine can have serious side effects, including bone marrow suppression, liver toxicity, and pancreatitis.
- Topical Therapies:
- Tacrolimus at 0.1% concentration can be applied topically to the perianal region once daily. An initial study showed complete remission in 5 of 10 (50%) patients and partial response in 4 of 10 (40%) patients; only 1 patient did not respond at all. A larger study showed complete remission over 16 weeks in 15 of 19 (79%) patients and marked improvement in the remaining 4 patients when used in combination with prednisone, a novel protein diet, and a short course of metronidazole. When tacrolimus is administered alone, complete remission has been reported for only 50% of patients. Because it is applied topically, this drug has the advantage of avoiding systemic immunosuppression. It is the author’s clinical opinion, based on experience and these studies, that tacrolimus is best when used as an adjunctive therapy rather than monotherapy or used as monotherapy for mild cases.
- Antibiotics: Secondary infections can accompany perianal fistulas and should be addressed appropriately with either systemic or topical (chlorhexidine) medication.
Surgical Intervention
Surgery usually included resection of all diseased tissue with or without removal of the anal sacs. This procedure could involve anywhere from a focal area of resection all the way up to a 360-degree resection with anoplasty. When a perianal fistula was believed to be associated with low tail carriage, amputation of the tail was also described as a treatment but is no longer recommended. The use of laser for surgical excision has been described, as has cryotherapy to ablate the diseased tissue. Typically, patients are given a stool softener postoperatively to lessen the pressure during bowel movements and to allow the area to heal.
If anal sacs are involved, then surgery may be necessary.
Alternative Therapies
Alternative therapies addressing wound healing have become popular as treatment options for perianal fistulas. One of the first evaluated therapies was intralesional injection of human embryonic stem cell-derived mesenchymal stem/stromal cells. More recently, the use of fluorescent light energy has been evaluated. This therapy requires weekly treatment to help decrease inflammation and increase wound healing. The recent commercialization of fluorescent light energy has made it more readily available to veterinarians. The author has used this treatment modality for several cases of perianal fistulas and noted both significant improvement of clinical signs and complete remission. Other therapies have been explored, including platelet-rich plasma (PRP) or stem cell injections and fluorescent light therapy.
Hygiene
Clipping of the perianal region to increase ventilation along with cleaning the area. Use unscented baby wipes to keep your dog's butt clean. Controlling bacteria is paramount when dealing with perianal fistulas in dogs.
Herbal Remedies
Some herbal remedies, such as quercetin and olive leaf extract have natural anti-inflammatory properties. Topical application of silver spray may also help provide relief and promote healing.
Prognosis and Long-Term Management
Perianal fistulas can be a severely debilitating disease, but most dogs respond well to therapy if started in a timely fashion. Depending on the therapy instituted, most patients will start to show clinical improvement within a few weeks. The fistulas may not be completely healed over, but other clinical signs should improve within that time. Recovery from perianal fistulas is often a long road, but many affected pets live long, good-quality lives. Most pets show improvement after a few weeks of therapy, but treatment is generally lifelong and requires regular monitoring.
Prognosis for initial healing early lesions is good; however, recurrence is common, particularly in dogs with moderate to severe disease. Effective preventive measures are not known. High quality diets may decrease the chance of inflammatory and allergic intestinal diseases, which are often associated with perianal fistulas.
Can a Perianal Fistula Heal on Its Own?
No. Perianal fistulas will not heal on their own and always require intervention by a veterinarian. If left untreated for a long period of time, they can become very serious and debilitating.
Lifespan with Perianal Fistula
Dogs with well-managed perianal fistulas can live a long and healthy life. While some dogs may experience more severe forms of the disease that may shorten their lifespan, the majority of affected dogs can achieve remission.